This invention relates to a face-to-face weaving machine comprising a cutting bench to guide the movement of a cutting blade in order to cut a face-to-face fabric, wherein said cutting bench is carried and/or supported at its extremities by the frame of the weaving machine.
In a face-to-face weaving machine, two fabrics are woven simultaneously one on top of another and they are connected to each other through pile warp yarns moving in a pattern -forming manner from the lower fabric to the upper fabric and vice versa.
Both fabrics are held at a distance from each other through the opening between the lower and upper cutting rod, provided that sufficient tension is put on the warp threads. Before being presented to the cutting movement, the non-separated face-to-face fabric will be kept apart over the distance between the upper and lower cutting rod. The cutting bench is provided with a knife carriage with cutting blade running back and forth over the cutting bench over the entire width of the fabric.
After cutting of the face-to-face fabric, both fabrics, i.e. the upper and lower fabric, are pulled out of the fabric area by a pull roll and evacuated respectively upwards and downwards.
The upper fabric lies at approximately 180° firmly against the (upper) pull roll (also called picker roll) in order to have good adherence to the pull roll so as to be evacuated under tension at a controlled speed without risk of slipping. Then, the upper fabric is guided over a guiding support that bends by 180° the upper fabric running out almost horizontally on the pull roll in order to stretch it out of the reach of the pull roll. There, the upper fabric is again bent by 90° to evacuate the fabric downwards, from where it is evacuated horizontally under the operator position together with the lower fabric (although with a shifted pattern because of the difference in distance run), in order to be led to the delivery location in the space behind the weaver.
The cutting bench that guides the cutting blade in its back and forth movement to cut the face-to-face fabric is located in the space bordered by the upper and lower pull roll, the face-to-face fabric and the vertically evacuated upper fabric. As all these parts are moving during normal operation of the weaving machine, the cutting bench can only be positioned by its extremities on the side frames of the weaving machine and this out of reach of the fabric.
At each cycle during the weaving process, after introduction of the one or more wefts, the weft yarns are pressed against the fabric border by the movement of the reed. This beat movement is accompanied by significant forces that generate vibrations and deformations on the machine frames. These vibrations and deformations are further transmitted to the cutting bench positioned on the machine frames. As the cutting bench cannot be supported between the machine frames, these vibrations and deformations, which are transmitted to the cutting bench from both sides of the machine frames, cause significant sagging of the cutting bench. This sagging becomes all the more significant with greater weaving speeds and when the force exerted during beat-up increases. The generated vibrations have a frequency of a multiple of the machine speed.
This leads to cutting of the face-to-face fabric in unequal upper and lower fabrics and uneven pile height in a carpet. As, at a same machine speed, sagging of the cutting bench remains constant at every position in the width of the weaving machine when the cutting blade passes through that position, this provides a wave-like character to the cut in lateral direction, whereas at every position in the lateral direction the pile height remains the same in longitudinal direction. At low weaving speeds, this defect only has a limited impact on the quality of the fabric.
However, at high fabric speeds and when significant forces are present due to the beat movement of the reed, this produces fabrics of lower quality, which must be submitted to expensive further processes to shave off the pile yarns that stand out above the other pile yarns, in order to obtain a fabric with even pile height. This is also a waste of expensive pile yarn material.
As already mentioned, at constant fabric speed, sagging of the cutting bench is constant at each position in the width of the weaving machine when the cutting blade passes through. This means that, at constant weaving speed, a wave effect is created in both fabrics (upper and lower fabric) in the lateral direction of the weaving machine, which at lower machine speeds is not immediately apparent to the eye.
However, when the machine is restarted after a stop and when full weaving speed is not yet reached in the first cutting cycle, this sagging pattern is no longer equal and on these fabric lines that are cut during starting of the machine, it will be clearly visible that pile height differs from the previously and subsequently cut fabric lines. In weft direction, this introduces unacceptable lines in the fabric. The so-realized fabrics are of lesser quality or they must be discarded.
To increase the stiffness of the cutting bench, it is known from German patent publication DE 3 104 970 that the shape of the cutting bench positioned by its extremities on the machine frame can be adapted. However, this solution reduces sagging of the cutting bench only to a limited extent.